The pair were heard discussing media coverage of the case including a suggestion that Loffley had been "studying up" on the Kahui case where twin babies were killed and their father Chris Kahui charged.

There have been a number of parallels between the cases - a father left alone with the children who died soon after, drug using families, indications of prior abuse, and defences that have sought to cast aspersions on the mothers' involvement.

Kahui was found not guilty but a coroner later made findings that strongly pointed the finger at him.

Loffley is charged with killing JJ on November 14, 2011, at the Lawrence's Orakei home.

The Crown says while Lawrence was out Loffley struck the boy so hard in the stomach it split his liver and pancreas in two.

Doctors said the injuries looked like they had been caused by a car crash.

In other phone calls played to the court, Loffley insisted JJ fell off a bed and his legs went over his head when he hit the ground.

Loffley suggested the boy died of brain damage or "it might be meningitis or something".

When Lawrence told him doctors determined it was internal bleeding in the abdomen, Loffley appeared surprised.

He later suggested it may have been from CPR efforts pressing too hard on JJ's stomach.

When police began investigating the pair in earnest Loffley was heard saying: "They're trying to put us against each other, aye baby."